Filament tensioning



Oct; 13, 1959' J. KUFFER FILAMENT musxoumc Filed Feb. 25. 1957 2Sheets-Sheet 2 A Fla. 7

Fla. 8

INMENTOR JOHANNES KUFFER PATENT AGENT United States Patent (NiceFILAMENT 'IiENSIONlNG Johannes Kiilfer, Ulm (Danube), Germany, assignorto Telefunken G.rn.b.H., Berlin, Germany ApplicationFebl-uary 2-5, 1957,Serial No. 641,922

7 Claims. (Cl. 313-273 The present invention relates to a method anddevice for tensioning the filament in an electron tube, particularly, adirectly heated electron tube, by means of a spring attached at one ofits ends to one end of'the filament and at its other end to a fixedpoint of the device.

Such arrangements have been known per se. In one of the known structuresof this kind, the filament is mechanically tensioned by providing adouble-arm supporting means for pre-tensioning the spring, whereby thearms of this supporting means originally form an angle of about 90. Oneof the arms is mounted on a fixed point of the structure and the otherarm is attached to one end of the spring, while the other end of thisspring is attached to the filament. After connecting the free end of thespring to the filament, the two arms of the supporting means are benttoward each other so that the springis mechanically biased, whereby thefilament is simultaneonsly'tensioned. This known tensioning device forfilaments in electron tubes has certain disadvantages, because theassembly is dependent to a certain extent upon the dexterity andreliability of the worker who may not uniformly tension all of thefilaments during mass production.

It is an object of the present invention to provide independence fromthese uncertainties in the manufacture and assembly of filaments inelectron tubes.

It is another object of the invention to provide a predeterminedmechanical spring bias in such devices and to release this bias aftermounting the filament.

It is a further object of the invention to attach the spring first to asupport and then bend the latter in such a manner that the springbecomes biased by distortion; subsequently to attach one of the ends ofthe support member to the tube structure and the free end of the springto the free end of the filament; and finally to bend or otherwise removethe bent end of the support member which end originally distorted thespring, thereby freeing the spring to tension the filament.

As a result of this, each filament will be under uniform tension,because the tension is dependent upon the predetermined mechanicalproperties of the spring. This support member becomes part of thestructure of the tube, the geometrical dimensions of which arestandardized during manufacture.

If the bent end of the support member biasing the spring is not removedto restore the spring tension, but is merely bent back to such extentthat it no longer contacts the spring, even when the filament expandsdue to heat, another purpose will be served. In this case, the end ofthe spring serves simultaneously as a mechanical stop for the spring,should the filament break. Indeed, considerable damage may occur withtubes of this type, due to sudden release of the spring in case of afilament break, the spring striking another structural element at adifferent electric potential and causing a discharge of the circuit viathe two elements. In most instances, the getter at anode potential willbe the element struck by the spring during its movement. This 2,908,842Patented Oct. 13, 1959 disadvantage is overcome by the method and thedesign according to the present invention.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

In the drawings:

Figures 1 and 2 illustrate side views of two different embodiments ofthe whole supporting structure accord ing to the invention, the tubesthemselves being not shown.

Figure 3 shows a front view of a support member used in the structureaccording to the invention, at one stage of its manufacture.

Figure 4 is a side view of the same support member illustrated in Figure3.

Figure 5 shows a side view of this support member at another stage ofits manufacture.

Figures 6 and 7 illustrate a modified embodiment of the support memberin front view and side view, respectively.

Figure 8 shows an assembly of the modified embodiment of the deviceaccording to this invention, in which the support member of Figures 6and 7 is employed.

Figures 4, 5 and 8 show only those parts of the tube structure which arenecessary to explain the invention.

In'Figures 1' and 2, 1 and 2 denote a lower and an upper sheet of mica,while 3 is a spacer member in the tube, for example, a supporting bar.One end of the heater filament 5 is secured to the lower mica sheet 1 bymeans of a filament holder 4. The upper end of the filament 5 ending ina small tab 8 is secured to a support device 6 by means of a whip spring7. This arrangement is shown in detail in Figures 3, 4 and 5.

If the support device 6 is associated with a whip spring 7, the formeris made of a U-shaped, punched metal sheet on which the spring 7 ismounted in such a manner that it extends parallel with respect to theportion of the sheet metal plate joining the two legs of the U. Thisspring 7 is spot-welded at 14 to one leg of the supporting device 6. Aside view of this device is shown in Figure 4. The U-shaped supportdevice 6 is subsequently bent at a right angle about the line 16, as isshown in Figure 5. For the sake of superior manufacture, the spring 7 iswelded to the support device 6 and the latter bent about the line 16 ina single operation. Since the spring 7 is mounted on one of the legs ofthe support device 6, the spring will be likewise bent to a right angle.The device, as shown in Figure 5, is now attached to the spacer 3 and tothe free end of the filament 5, for example, by spot-welding (see Figure1). After the parts have been assembled in this manner, it is merelynecessary to release the spring 7 which, according to the embodimentshown in Figure 1, is effected by bending back the upper part or leg ofthe support device 6 to the position 9, shown in dot-dash lines. Thebent back portion at 9 of the support device 6 serves now as a stop forthe spring 7 in case of a filament break. If, in such a tube a getter10, which may be at anode potential, is provided and located as shown inFigure 1, the spring 7, when suddenly freed, will be prevented fromstriking this getter 10 during the sudden upward movement.

If such mechanical protection is not necessary, the free end of thesuspending device 6 may be removed by cutting off this metal pieceeither at 15, 16 or 17 (see Figure 3). The assembled support device 6,in case of this modification, is shown in Figure 2. In case of a breakof the heater filament 5, the spring 7 suddenly snaps upwardly to theposition indicated in a dash-dot line at 11 moving through an are 12.

In the embodiment illustrated in Figures 6, 7 and 8, the spring securedto the filament is designed as a coil spring. According to Figure 6, asupport device 18 constituting a sheet metal stamping in the'shape ofthe letter E is provided, and a coil spring 19 is placed on the centerleg 22 thereof. The two outer legs 20 and 21 of this support 18 serve asabutments for the two spring ends. One of the spring ends may beattached to one of the outer legs, for example, by spot-welding at 12a,to the leg 20, while the other leg 21, in substantially the same manneras in Figures 1 and 2, will be either bent (see Figure 8) or cut 011after the filament has been secured to the distorted spring 19. In caseof a break of the heater filament 5, the upper end portion of the spring19 snaps back to a limited extent only, because the angular displacement23 of this spring portion is limited by the bent leg 21 serving as astop for the spring portion, so that the getter cannot be struckthereby.

I claim:

1. The method of mounting a filament without tension between a fixedholder and a spring and then tensioning the filament, including thesteps of predistorting the spring through a selected distance within theelastic limit of the spring by applying a distorted member directlybetween the extremities of the spring, holding the spring so distorted,connecting the untensioned filament between the holder and thepredistorted spring, and subsequently releasing the spring by displacingthe distorting member.

2. A tensioning device for use in mounting a filament in an electrontube having a filament holder to which one end of a filament is fixed,comprising a support member having one leg fixed in the tube and spacedfrom said holder and having another leg bent toward said holder;

a spring attached to said fixed leg and having a free end distortedtoward the holder and maintained thereat by said bent leg, the free endof the spring being joined to the free end of the filament prior torelease of the spring by retraction of the bent leg.

3. In a device as set forth in claim 2, said bent leg when retractedbeing moved only out of contact with the spring but left adjacentthereto to act as a spring stop in the event of filament breakage.

4. In a device as set forth in claim 2, the bent leg being broken ofiduring said retraction.

5. In a device as set forth in claim 2, said support member being aU-shaped sheet metal stamping, and said spring being a whip springsecured to one leg of the U and distorted by bending of the other leg ofthe U to maintain the spring arched.

6. In a device as set forth in claim 2, said support member being anE-shaped sheet metal stamping, and said spring being a coil springmounted around the center leg, one end of the spring resting against ontoutside leg and the remaining leg being bent over to bias the free endof the spring toward the filament holder.

7. In a device as set forth in claim 2, the spring being mounted on thesupport member before being distorted by bending of said leg.

References Cited in the file of this patent UNITED STATES PATENTS1,615,654 Ryder Ian. 25, 1927 1,657,221 7 Metcalf Jan. 24, 19281,720,442 Robinson July 9, 1929 2,092,886 Kiihle Sept. 14, 19372,506,895 Sassaman May 9, 1950 2,770,753 Moesker Nov. 13, 1956 2,789,243Gowell Apr. 16, 1957

